Circuits to control and drive brushless DC (BLDC) electric motors are known. In some arrangements, the circuits provide a phase advance of drive signals that drive the electric motor, the phase advance related to rotational speed of the electric motor or related to a measured motor total current. However, such circuits are only able to provide one relationship, or a small number of relationships, between phase advances and rotational speeds, in addition, external components and pins of a motor control integrated circuit (IC) may be required to set the parameter for each electric motor or each electric motor application.
Some known electric motor drive circuits are described in U.S. Pat. No. 7,590,334, issued Sep. 15, 2009, U.S. Pat. No. 7,747,146, issued Jun. 29, 2010, and U.S. patent application Ser. No. 13/271,723, filed Oct. 12, 2011, all of which are incorporated herein by reference in their entireties and assigned to the assignee of the present invention.
A BLDC electric motor can exhibit different efficiency behaviors versus speed when used in different applications. For example, the same BLDC electric motor can be used with different fan blade arrangements in different applications. Different types of BLDC electric motors can also exhibit different efficiency behaviors versus speed.
Motor noise, vibration, and efficiency are influenced by a variety of characteristics. One such characteristic is a phase of currents that appear in the motor windings relative to a rotational position of the motor. Particularly as a motor speed increases or decreases, the phase of the currents can lag or lead, respectively, a reference rotational position of the motor. Also, at high motor speeds, the current in the motor windings can tend to lag the reference position of the motor.
In view of the above, it would be desirable to provide an electric motor control circuit and associated method that can detect a phase of a current in a motor winding, for example, by detecting a zero crossing of the current.